1. Field of the Invention
The invention relates generally to electric power distribution panelboards/switchboards and in particular to a panelboard/switchboard assembly accommodating both plug-in and bolt-on type modules.
2. Prior Art
Circuit breakers and disconnect switches for power distribution panelboards or switchboards may be plug-in type or bolt-on type. Panelboards and switchboards have been designed and manufactured to accept either bolt-on or plug-in circuit breakers and disconnect switches. Manufacturers of panelboards and switchboards have an interest in standardizing the design of panelboards into one common platform to reduce manufacturing and inventory costs. Customers have an interest in a common platform to provide flexibility in changing from one type of circuit breaker or disconnect switch to another in the field.
One approach to accommodate both plug-in and bolt-on modules is described in U.S. Pat. No. 3,356,906. Interchangeable connections are made using specially shaped connectors with a free end extending across the panelboard to connect with bolt-on modules and a blade extension for connection with plug-in modules. Since the free end of the connector is not supported, the connector tends to turn and twist under the force to connect a plug-in module as well as under the weight of the module itself. Additionally, modules must be equipped with custom built-in slots to receive the blades. U.S. Pat. No. 4,358,815 describes another design to accommodate both bolt-on and plug-in modules. While these prior art designs are well suited for the intended applications, there is a need in the art for improved panelboards that can receive a variety of modules using a minimal number of components.